Several categories of safety devices implanted along highways exist at the present time.
A first category is that of slide rails or safety rails deformable in the event of shock, which are generally constituted by metallic sections.
A second category is that of safety barriers constituted by low walls made of reinforced or pre-stressed concrete which undergo neither deformation nor displacement in the event of a shock of a vehicle.
A third category is that of conventional roadside curbs.
Safety rails attempt to slow down a vehicle out of control by absorbing its kinetic energy by deformation of the rail, but this effect is inefficient as soon as the mass and/or speed of the vehicle are high. The safety rails are dangerous for motocyclists who strike them.
The metal-on-metal friction at the moment of the shock creates a very strong deceleration and a transfer of energy towards the rail which compromises the resistance and efficiency thereof.
Safety barriers are very efficient to avoid a vehicle accidentally leaving the highway. On the other hand, they are very aggressive for the vehicle since the kinetic energy of the vehicle is absorbed by the crushing of the bodywork. Concrete safety barriers are expensive and they are long to install. Moreover, a vehicle which strikes a safety barrier overturns since the front wheels scale the wall due to the high coefficient of friction of the tires on the concrete. For the same reason, out-of-control vehicles often scale the concrete curbs.
U.S. Pat. No. 3,658,300 (TEMPLETON) describes safety devices for highways which are composed of steel sheets which comprise one or two concave lateral sides of which the lower edge is extended by a substantially horizontal apron placed on the ground. The aprons comprise on their rear face anchoring means which are embedded in the ground.
German publication No. DE A 2 148 219 (MEUGE) describes safety rails for highways which comprise an endless band which is connected to a fixed support by vertical rollers or by balls.
U.S. Pat. No. 3,519,249 (NAVE) describes safety rails which comprise a steel section placed on support posts. This section bears on its face turned towards the highway a deformable trough which contains a lubricating oil. In the event of shock by a vehicle, the oil lubricates the surfaces of the vehicle and of the rail which are in contact with each other, this facilitating slide of the vehicle against the rail.
U.S. Pat. No. 2,279,942 (HAUSHERR) describes safety devices .for highways of which the material has not been specified. These devices comprise, towards the road, a concave side and, to the rear, a vertical wall. This side and wall define a space in which is housed a longitudinal tank which contains an oil. Wicks passing through ports in the concave side are immersed in the oil and continuously pour drops of oil on the concave side.
Swiss Patent No. CH A 429 806 (BUCHER) describes safety devices for highways which comprise a rail made of concrete, steel or a light metal, which is connected to the supports by a damping device constituted for example by a spring or by easily deformable concentric tubes or by stirrup-shaped elements filled with a cellular body. The rails may be combined with curbs presenting a concave surface. These prior art documents show that it is known to lubricate with an oil the contact surface between a vehicle and the rails in order to reduce the coefficient of friction. However, the use of a lubricant liquid, although known, has few practical applications as difficulties in implementation are encountered.
If a tank and wicks, which permanently distribute the oil, are used, the consumption of oil is high unless it is recovered and recycled, which involves expensive installations.
If, as proposed in U.S. Pat. No. 3,519,249, a deformable trough located against the inner face of the rail is used, at the spot where the vehicle strikes, this trough, on breaking, creates roughness which risks blocking the crashed vehicle, instead of providing optimum slide, and fragments may injure the occupants of the vehicle. Moreover, the instantaneous projection of the oil at the location of the shock is random.